1. Field of the Invention
The present invention relates to a composite formed by including metal matrix such as titan or titan alloy with reinforcing fiber such as carbon fiber, more particularly to a composite in which the reinforcing fibers have end parts or to a composite having joint parts.
2. Description of the Related Art
Heretofore, composites formed by combining plural materials have been used widely. Composites are used for parts or members used under particularly severe condition since a composite having characteristics appropriate for a specific use can fabricate by selection of materials, compositions or methods of processing. Metal matrix composites such as titan matrix composite (TMC) have been intensively studied and developed for parts requiring high specific strength and high specific rigidity. The composites are reinforced in such a way that reinforced materials typified by ceramic fibers such as silicon carbide or alumina fiber are mixed with metal matrices comprising metals or metal alloys.
Forming preform when composing each of raw materials is the particularly important process in fabrication of the composite. The following four ways are usually employed.
{circle around (1)} A way comprising aligning reinforcing fibers in one direction, fixing the aligned fibers with organic binder or the like and sandwiching the bound fibers between metal matrices.
{circle around (2)} A way comprising aligning reinforcing fibers in one direction and fixing the aligned fibers by weaving with metal (metal alloy) foil.
{circle around (3)} Away comprising vapor-depositing metal matrix on to the surface of reinforcing fibers by physical vapor deposition (PVD method).
{circle around (4)} A way comprising winding reinforcing fibers on a drum and fixing the reinforcing fibers by thermal-spraying metal (metal alloy) on the surface thereof.
Above all, the way of composing to form preform by sandwiching bundles of reinforcing fibers between metal matrices where reinforcing fibers have been agglomerated together in advance such as a way of fixing reinforcing fibers with organic binder or a way of fixing reinforcing fibers by weaving with metal (metal alloy) foil is widely employed because of inexpensive cost and simple processing.
For example, when fabricating a tape type composite, flat cloths of reinforcing fibers such as carbon fibers are sandwiched between tape type continuous metal matrices such as titan or titan alloy to form a preform, which is then hot-pressed. If necessary, the preform is rendered to hot isostatic pressing (hereinafter referred to as HIP) under the condition of high pressure and high temperature in a sealed pressure vessel to form a tape type composite.
Such HIP processing is performed as follows.
The tape type preform is sealed into a HIP pressure vessel and set to an initial pressure and temperature. In case of Ti-4.5Al-3V-2Fe-2Mo alloy, an initial pressure is approximately 30 kg/cm2 and temperature is approximately 400xc2x0 C. The process is followed by gradual heating until not lower than the temperature where stress decreases to cause plastic deformation that is a high temperature region of HIP processing temperature to keep. An appropriate temperature in case of Ti-4.5Al-3V-2Fe-2Mo alloy is approximately 750-850xc2x0 C., or more preferably approximately 775xc2x0 C.
After heating to a predetermined temperature, pressure is increased to approximately 1200 kg/cm2, the condition is kept for about 2 hours and then both of the pressure and temperature are decreased.
An annular composite can be made by HIP processing from the convolved tape type preform thus fabricated.
However, in case of the continuous tape type preform, there are indispensably end parts of reinforcing fibers arising when processing, for example, removing defective parts or when cutting in a predetermined length. Treatment of thus arisen end parts has been a problem. Conventionally, as shown in FIG. 5, vertical cut ends 15 of the end parts of reinforcing fibers are joined together; the joined part is sandwiched between upper metal matrix and lower metal matrix and processed by means of hot-press or HIP to fabricate a composite 16.
In thus formed composite, a part where reinforcing fibers sandwiched between metal matrices is vertically cut, that is a joined part of reinforcing fibers is extremely low in strength. As a result, the composite has low strength and poor reliability as a whole so that it is difficult to supply stable and high performance material.
Especially when an annular composite, which is often applied to aircraft engine, is fabricated by HIP process from the tape type preform, the cutting ends 15 in the annular part involve the risk of rupture of the material itself through generation of cracks owning to repeated stress which is loaded to the composite even if the stress is under the elemental strength of the composite 16.
In view of the need to solve the prior problems, the present invention has an object to provide a metal matrix composite having stable performance without extremely weak portions and capable of assuring strength with a simple structure.
To solve the problems, in one aspect of the present invention, a metal matrix composite formed by hot-pressing or hot-isostatic-pressing a flat formation of reinforcing fibers sandwiched between metal matrices comprises a joined end part in the longitudinal direction of reinforcing fibers which is joined obliquely at an aspect ratio within the approximate range of 2:1 to 1:10 on the basis of the direction of the width of reinforcing fibers to the longitudinal direction of reinforcing fibers.
In another aspect of the present invention, a metal matrix composite formed by hot-pressing or hot-isostatic-pressing a flat formation of reinforcing fibers sandwiched between metal matrices comprises a joined end part in the longitudinal direction of reinforcing fibers which is joined obliquely at a joining angle of 5 to 60 degrees with respect to the longitudinal direction of reinforcing fibers.
The present invention provides a composite which is composed in such a manner that the end part of reinforcing fibers are cut in an oblique direction, the obliquely cut faces are joined together, the joined part of reinforcing fibers is sandwiched between metal matrices, and thus integrated part of metal sandwiched fibers is hot-pressed or hot-isostatic-pressed. Thus, a composite having stable performance and reliability, which does not give rise to lowering of strength against the stress perpendicular to the longitudinal direction of fibers can be provided.
The metal matrix composite according to the invention can be fabricated with reduced cost because the composite have extremely simple structure.
The joining angle is preferably 5 to 60 degrees or more preferably 5 to 45 degrees or the aspect ratio is preferably in the approximate range of 2:1 to 1:10.
That is because if the ratio difference of the aspect ratio is larger than about 1:10 or the joining angle is less than about 5 degrees, the strength of the reinforcing fibers in themselves lowers, if the ratio difference of the aspect ratio is smaller than about 2:1 or the joining angle is greater than about 60 degrees, the overlap length of the joined part is so short that the fact causes lowering of strength of the reinforcing fibers.
According to yet another aspect of the present invention, in a metal matrix composite formed by hot-pressing or hot-isostatic-pressing a flat formation of reinforcing fibers sandwiched between metal matrices, a plurality of metal matrices and a plurality flat formations of reinforcing fibers are lapped each other to form layers of metal matrices and flat formations of reinforcing fibers so that the adjacent upper layers of flat formations of reinforcing fibers and the adjacent lower layers of flat formations of reinforcing fibers to a layer having a joined part of flat formations of reinforcing fibers are continuous and have no joined parts.
For example, when a joined part of reinforcing fibers comes to the surface part of the composite, cracks tend to occur from out side where stress is easily transferred. The joined part position should be a middle position with respect to the lapping direction so as to be protected by the upper and lower layers of continuous reinforcing fibers, preventing from lowering of strength. Thus, more reliable quality assurance is possible.